[cfe-dev] -fdenormal-fp-math

[Hal Finkel via cfe-dev]

On 03/17/2017 10:19 AM, Evandro Menezes wrote:
> On 03/17/2017 10:13 AM, Stephen Canon wrote:
>>> On Mar 17, 2017, at 10:40 AM, Hal Finkel via cfe-dev 
>>> <cfe-dev at lists.llvm.org> wrote:
>>>
>>>
>>> On 03/17/2017 09:37 AM, Evandro Menezes wrote:
>>>> On 03/16/2017 02:09 PM, Hal Finkel wrote:
>>>>>
>>>>> On 03/16/2017 12:43 PM, Evandro Menezes wrote:
>>>>>> Hal,
>>>>>>
>>>>>> Would it be feasible for clang to generate crtfastmath.o on the 
>>>>>> fly at link time, by using LLVM to emit the object file?
>>>>> We could. We could also just inject the necessary IR into each 
>>>>> module as a linkonce_odr initialization function. I'm not sure it 
>>>>> is worthwhile; we depend on compiler-rt for a lot of optional 
>>>>> features.
>>>> OTOH, by making sure that a module contains this code when any 
>>>> function is relaxing the FP semantics, even if the link command 
>>>> line doesn't include -ffast-math, the expected behavior can be 
>>>> guaranteed.
>>> I'm not sure that's desirable. The problem is that these are global 
>>> settings, and so we need to decide whether the flag on any 
>>> translation unit will affect all others, or if we need the flag at 
>>> link time for something that affects the entire application. I lean 
>>> toward the latter.
>> Right; setting fast-math on one translation unit should not effect 
>> the behavior of another translation unit.
>
> Got it.
>
> So, right now this only works if libgcc is available.  Would it be a 
> good idea to add it to compiler-rt when it is not?

Sounds reasonable to me.

  -Hal

>
> Thank you,
>

-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory